1. Field of the Invention
The present invention relates generally to image projection, image scanning and image printing systems and more particularly to a method of controlling resolution and exposure to improve image quality using imaging array technology.
2. Background of the Invention
Light valves, such as micro-electro-mechanical systems (MEMS) and liquid crystal displays (LCD), have been used in image exposure processes to expose light sensitive media in patterns prescribed by rows and columns of the light valve modules. Typically, the desired image is defined by light valve modules activated to illuminate the light sensitive media directly. The resolution and pitch of the light valves typically determines the resolution and pitch limitations of the image.
FIG. 1, adapted from U.S. Pat. No. 4,560,994 issued to Sprague, shows typical optics configurations for scanning imaging information onto an external drum device 20. A light source 10 is used to project an image. Optics 12, 16, 24 and a light modulator 14, are required to produce an image.
The general configuration of a light valve array 14 is shown in FIG. 1. The array is organized in columns and rows of individual light valves, with a space or gap between the light valves. The columns and rows are in a straight line and have the same pitch throughout the array. The pitch of an array is its light valve size plus the gap size. The pitch is defined herein as the distance from center to center of adjacent light valves.
This type of array requires a gap between light valves on the grid to minimize cross talk and avoid mechanical defects. The size of the gap between light valves has a direct impact on the image quality for projected, scanned and printed images. Large gaps reduce the quality of projected images and reduce the resolution of the printed image.
Efforts have been made to increase resolution by reducing the light valve dimensions and light valve gap. The resulting small light valves with small gaps pass lower levels of transmitted or reflected light, thus reducing the brightness level of the projected image and the amount of light energy reaching the photosensitive media.
One method and apparatus for exposure control of images formed by two dimensional light valve arrays is described by Gelbart in U.S. Pat. No. 5,132,723. The ""723 patent describes a method and apparatus for exposure control in which the intensity variation between rows of light valves due to defective light valve modules is compensated for by deliberately deactivating non-defective light valves. In this method, a depression in the light intensity profile caused by a defective light valve is adjusted by deliberately inhibiting or turning off functional light valves in other rows. As a result, the intensity profile is uniformly depressed across the light valve rows when a single light valve is defective.
Another method and apparatus for exposure control of images formed by two dimensional light valve arrays is described by Gelbart in U.S. Pat. No. 5,049,901. The ""901 patent describes a method in which large area light sources are used with deformable mirror devices to illuminate light sensitive material. This method employs a driver circuit and position transducer to scan light sensitive media relative to an array of light valves that are illuminated by a large area light source. By focusing the reflected light from the activated light modules, image resolution is provided with the desired intensity and energies afforded with large area light sources.
Many industrial applications require an imaging device to be capable of multiple resolution output. Current light valve technology is not able to meet this requirement without costly optical realignment. Changing the resolution available with a light valve currently requires the expensive variable optics and time consuming adjustments in the projector, imager, or detector.
There remains a need for electronic control of resolution and exposure using a light valve modulator without the use of expensive variable optics in a variety of applications, including image projection, detection and printing. Furthermore, there remains a need in the art to obtain high resolution using a light valve modulator.
The present invention provides an imaging system that comprises a surface for receiving an image, and a light modulator. The light modulator comprises a plurality of light valves in a two-dimensional array that has orthogonal rows and columns in a Cartesian coordinate system with first and second orthogonal axes. The columns are arrayed along the first axis in the coordinate system and the rows are arrayed along the second axis. A certain number of rows in the modulator form a segment. In the imaging system, the surface is transported relative to the modulator in a direction along a transport axis. The first axis and the transport axis form an angle xcex1 other than 90xc2x0, this angle xcex1 is inversely proportional to the number of rows in each segment. The number of rows in the segment is n, and n is an integer that is greater than 1. The modulator has at least 2 segments, and each light valve has an X dimension along the first axis and a Y dimension along the second axis. The light valve dimensions are equal, X=Y, and the angle xcex1=tanxe2x88x921(1/n).